Sialon, the ultimate product of the process of the present invention, is useful in making valve components in coal gasifiers and in the manufacture of gas turbine engine components and metal die cast molds. Furthermore, sialons having good thermal shock and thermal creep, high strength and good oxidation resistance are candidate materials for high temperature applications.
It is well known in the prior art to make sialon, which is also known as silicon aluminum oxynitride, from a mixture of silicon nitride and alumina and also from a mixture of silicon nitride, alumina and alumina nitride. Illustrative of a prior art process utilizing silicon nitride, alumina and aluminum nitride as starting materials in U.S. Pat. No. 4,066,468 to Kamigaito et al. One of the difficulties with this type of approach to the manufacture of sialon is that silicon nitride is expensive. Thus, there has existed in the art a need for a less expensive starting material. Exemplary of a prior art process which does not use a metal nitride as a starting material is U.S. Pat. No. 3,991,166 to Jack et al., which discloses the use of silicon and alumina as starting materials, and which uses boron nitride to protect against surface degradation of the sialon (column 9, lines 59-64). Another prior art patent of interest in this area is U.S. Pat. No. 3,572,992 to Komeya et al., which is directed to manufacturing a molded and sintered mass of aluminum nitride. None of the prior art of which I am aware discloses a process using silicon, alumina and either aluminum or aluminum nitride as starting materials in a controlled nitriding step to produce a metastable precursor powder having about 20 to 60 percent of the silicon thereof in the nitride form and for converting this precursor powder to sialon using a controlled sintering process.